Windows Regsvr32.exe Executed with Suspicious File Extension Masquerading as DLL

Alerts when REGSVR32.exe runs with a command-line argument ending in a suspicious masquerade file extension.

FreeReviewedSigma · High · v1

Product: windows
Category: process_creation
Author: Florian Roth (Nextron Systems), frack113 (SigmaHQ), DRL 1.1
Published: 2021-11-29
Updated: 2026-07-30

ATT&CK techniques

Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
- T1218.010Regsvr32
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags process creation events where REGSVR32.exe is executed and the command line ends with one of several file extensions commonly used for masquerading. Attackers may abuse regsvr32 to load a DLL via a crafted argument while disguising the payload filename with a benign-looking extension. The detection relies on Windows process creation telemetry, including the executable image/filename and the full command line suffix.

Reporting behind it

Related detections9 linkedT1218.010 — drag to rearrange

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Masquerading SSLoad PhantomLoader DLL Execution via Regsvr32 Silent Load from AppData (via process_creation)

Malicious Kimsuky AlphaSeed Payload Execution via Regsvr32 Loading edge dat (via process_creation)

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HttpSpy Payload Registration via Regsvr32 of Non-DLL File (via process_creation)

Malicious regsvr32 Scriptlet Execution via scrobj.dll

Windows Regsvr32.exe Executed with Suspicious File Extension Masquerading as DLL

Pivot detection · T1218.010 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

windows-regsvr32-exe-executed-with-suspicious-file-extension-masquerading-as-dll-089fc3d2

title: Windows Regsvr32.exe Executed with Suspicious File Extension Masquerading as DLL
id: 467147ba-50c5-49e6-9e0e-8ad2120ee55d
related:
  - id: 8e2b24c9-4add-46a0-b4bb-0057b4e6187d
    type: obsolete
  - id: 089fc3d2-71e8-4763-a8a5-c97fbb0a403e
    type: derived
status: test
description: This rule flags process creation events where REGSVR32.exe is executed and the command line ends with one of several file extensions commonly used for masquerading. Attackers may abuse regsvr32 to load a DLL via a crafted argument while disguising the payload filename with a benign-looking extension. The detection relies on Windows process creation telemetry, including the executable image/filename and the full command line suffix.
references:
  - https://thedfirreport.com/2021/11/29/continuing-the-bazar-ransomware-story/
  - https://blog.talosintelligence.com/2021/10/threat-hunting-in-large-datasets-by.html
  - https://guides.lib.umich.edu/c.php?g=282942&p=1885348
  - https://harfanglab.io/insidethelab/uac-0057-pressure-ukraine-poland/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_regsvr32_susp_extensions.yml
author: Florian Roth (Nextron Systems), frack113, Huntrule Team
date: 2021-11-29
modified: 2025-08-27
tags:
  - attack.stealth
  - attack.t1218.010
logsource:
  category: process_creation
  product: windows
detection:
  selection_img:
    - Image|endswith: \regsvr32.exe
    - OriginalFileName: REGSVR32.EXE
  selection_cli:
    CommandLine|endswith:
      - .bin
      - .bmp
      - .cr2
      - .dat
      - .eps
      - .gif
      - .ico
      - .jpeg
      - .jpg
      - .log
      - .nef
      - .orf
      - .png
      - .raw
      - .rtf
      - .sr2
      - .temp
      - .tif
      - .tiff
      - .tmp
      - .txt
  condition: all of selection_*
falsepositives:
  - Unlikely
level: high
license: DRL-1.1

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